This invention concerns the field of production of oil and other reservoir fluids from subterranean reservoirs, and particularly the use of gas-lift well systems. The invention provides a new method for trouble-shooting gas-lift wells. It allows detection of leaks in production tubing and casing without the use of wireline tools, and it is particularly useful for determining whether the valves in a gas-lift well are operating properly.
Prior methods of detecting leaks in wells have involved the use of wireline tools. For example, U.S. Pat. No. 2,383,455 discloses a method for detecting casing leaks in a subterranean well by measuring the temperature gradient of the well. A thermal recorder is lowered through the production tubing in the well to measure the temperature gradient of the well. A temperature anomaly at a given depth is indicative of a leak at that depth. It is also known in the art to use other wireline tools, such as mechanical calipers, sonic, or noise detection tools, to detect tubing and casing leaks in wells.
Such wireline tool methods have several disadvantages for the well operator. The methods are usually performed by a well service company on a contract basis, which involves additional operating costs and lost time during well evaluation. It is usually necessary to shut down operations on the well, at least during insertion and removal of the tools. Specialty tools are used, and interpretation of the results often requires expert analysis. There is also some risk associated with inserting tools into a well, since if the tool is irretrievably lost in the well, it may be necessary to implement expensive remedial operations, or abandon the well. Consequently, the expense and risk associated with using these wireline tool methods are significant disadvantages for the well operator.
A method which does not involve the use of wireline tools has been developed for detecting casing leaks in underground storage caverns. U.S. Pat. No. 4,474,053 discloses a method for detecting casing leaks in an underground cavern used to store hydrocarbons. An inert gas is maintained under pressure in the annulus between two casings, and the pressure of the inert gas is continuously monitored at the wellhead. A decrease in pressure of the inert gas at the wellhead is indicative of a leak in the casing.
In the subject invention, a new method is disclosed that allows detection of production tubing and casing leaks in gas-lift wells, without the use of wireline tools. The method may also be used to detect whether gas-lift valves on the production tubing in a gas-lift well are open or closed. This new method eliminates the cost and risk associated with the use of wireline tools. The method is also simple, and easy for field personnel to perform with minimal equipment. The results obtained are easy to interpret, allowing operating personnel to troubleshoot wells at the well site and without the need to consult off-site experts.